Fast drying duplicating ink

The present invention relates to duplicating inks, and more particularly to water-in-oil emulsion duplicating inks.

Water-in-oil emulsion inks are formulated with an oil phase surrounding water phase droplets having a pigment, such as carbon black, dispersed therein. Such formulations are well-known in the art, and are disclosed, for example, in U.S. Pat. Nos. 2,839,412, 3,421,910, and 3,823,020.

Water-in-oil emulsion inks are generally used in digital duplicating processes. In those processes, the ink is introduced into a cylinder having a plurality of small holes. The cylinder is covered with a metal mesh, and a stencil is fixed upon the mesh. During the printing process, the ink penetrates through the holes in the cylinder onto the surface of a paper. The paper is held in contact with the cylinder by means of a platen roller.

The fibers of the paper have numerous small pores, which act to break down the two phases in the ink as the ink is absorbed into the paper. Generally, the oil phase is absorbed into the paper, and diffuses vertically and horizontally. The water in the water phase diffuses vertically and horizontally, and evaporates. The pigment particles remain on the paper surface until the water evaporates. At that time, the pigment particles are drawn from the paper surface into the paper by the oil. The drying oils (such as china-wood oil and aged linseed oil) form an oil film on the paper fibers and carbon black particles, and air oxidation of the drying oils then slowly occurs. The pigment particles absorb the oil, thus limiting the vertical and horizontal diffusion of the oil, and hence, the printed images. The diffusion of the oil containing the pigment particles is dependent upon both the time needed for the oil to dry, and the quality of the paper. The drying time for the oil is affected by the speed at which the oil is oxidized on the surface of the paper fibers by air. This process, however, is quite slow. Since the amount of diffusion relates directly to print quality, it is desirable to minimize diffusion.

To that end, various techniques have been tried to increase the rate at which water-in-oil emulsion inks dry upon application to a paper substrate. Surfactants have been added to the water phase of the ink compositions to reduce the surface tension of the water and thereby promote evaporation. The amount of low volatility liquids in the oil phase has been reduced. Drying agents have also been added to both the water-in-oil phases to increase the drying rate. However, conventional water-in-oil emulsion ink compositions, including those containing the above noted surfactants, reduced amounts of low volatility liquids, and drying agents, still exhibit slow drying times on various papers, as well as an unacceptable amount of pigment diffusion.

Thus, there exists a need for an water-in-oil emulsion ink composition that dries quickly and exhibits minimal pigment diffusion when printed on paper for varying qualities. There is also a need for an water-in-oil emulsion ink composition that exhibits improved stability.

The water-in-oil emulsion ink compositions of the present invention solve the problems associated with prior art water-in-oil emulsion inks, and achieve distinct advantages thereover. The ink compositions of the present invention comprise a water phase comprising water and a dispersion containing oxidized carbon black, and an oil phase comprising a saturated oil and an unsaturated oil. Preferably, the carbon black is oxidized in an aqueous dispersion. The water phase may also optionally contain a surfactant, while the oil phase may contain, in addition to the saturated and unsaturated oils, an emulsifier, a viscosity adjusting agent, a surfactant, and a varnish.

The ink compositions of the present invention dry quickly, and exhibit minimal dispersion in the paper upon which the ink is applied. The ink compositions of the present invention remain liquid for extended periods of time upon exposure to the atmosphere.

It is believed that the oxidized carbon black particles in the water phase contact the unsaturated oil in the oil phase shortly after the ink composition is applied to the paper. The oxidized carbon black particles in turn oxidize the unsaturated oil, causing crosslinking in the oil, and resulting in accelerated drying.

Water Phase Components

Carbon Black

Essentially any commercially available aqueous carbon black dispersion may be used in the ink compositions of the present invention. Preferably, the dispersion contains carbon black in an amount from about 20% to about 50% by weight of the dispersion and the dispersion has a pH from about 7 to about 10. Also, the particle size of the carbon black is preferably from about 13 nm to about 100 nm. Carbon black dispersions useful in the ink compositions of the present invention include Permablack 292 and Permablack 1180, available from Mono-Chem Corporation, and AJACK BLACK 3017 and AJACK BLACK 3018, available from Solution Dispersion, Inc. Permablack 292 is preferred.

The amount of oxidizing agent used must be sufficient to effect substantial oxidation of the carbon black surfaces. Generally, when hydrogen peroxide is used as the oxidizing agent, the aqueous carbon black dispersion is present in a weight ratio of dispersion to aqueous hydrogen peroxide solution of about 1:2 to about 1:2.75. A dispersion/aqueous hydrogen peroxide solution weight ratio of approximately 1:2.35 is preferred. On a total ink composition basis, the carbon black dispersion is generally present in a weight ratio of carbon black dispersion to ink composition of about 1:3.2 to about 1:7.8.

Oxidation of the Carbon Black

The carbon black in the aqueous dispersion can be oxidized by mixing the dispersion with an aqueous solution of hydrogen peroxide. The concentration of the hydrogen peroxide in the aqueous solution should be from about 3% to about 30% by weight of the aqueous solution, with an amount from about 3% to about 5% by weight being preferred. More stable ink compositions are achieved when lesser amounts of hydrogen peroxide are used. It has been found that use of a hydrogen peroxide concentration of approximately 2.3% by weight of the water phase without solids will effect substantial oxidation of the carbon black and will therefore provide inks that are quite stable and exhibit fast drying times.

The mixture of the aqueous carbon black dispersion and the aqueous hydrogen peroxide solution comprises the water phase of the ink compositions of the present invention. Once the carbon black dispersion and the aqueous hydrogen peroxide solution are mixed to oxidize the carbon black, it is preferred that the oxidized carbon black remain in an aqueous dispersion and is not allowed to dry. The oxidized carbon black surfaces have many active species, such as --COOH, or C--OO--CH 3 , which are unstable when exposed to the atmosphere in the dry condition or when the environment temperature changes. Thus, changes in the temperature or in the environment are preferably also avoided.

To ensure sufficient oxidation of the carbon black, the mixture containing the carbon black and the hydrogen peroxide (i.e., the water phase) should be "aged" for a period of time ranging from 1 day to about 14 days prior to combination with the oil phase and use in printing operations. Increased aging time generally results in an ink composition having a faster drying time when applied to paper. Aging more than three (3) to six (6) days, however, provides only a marginal increase in drying time.

The carbon black in the dispersion may also be oxidized by pumping a mixture of a carbon black dispersion and deionized water (i.e., the water phase) through a vessel containing ozone. The mixing weight ratio of the carbon black dispersion to the deionized water is from about 1:2 to about 1:2.75, with a ratio of 1:2.35 being preferred.

Again, to ensure sufficient oxidation, the carbon black should be exposed to ozone for a time period ranging from about 1 hour to about 40 hours. The carbon black may be exposed to ozone for longer than 10 hours, but it is not believed that exposure beyond 10 hours causes any increase in drying rate.

Oil Phase

Saturated Oil

Saturated oils are used in the inks of the present invention to prevent the ink from drying in the open air and to control ink viscosity. The saturated oils that are useful in the inks of the present invention include naphthenic saturated oils. The preferred saturated oil for use in the ink compositions of the present invention is available under the trademark Tufflo-2000, from EMCO Chemical Distributors, Inc.

Unsaturated Oil

Unsaturated oils useful in the ink compositions of the present invention include China-wood oil, aged linseed oil, and other known drying oils. To be useful, the unsaturated oil should have a high number of conjugated unsaturated carbon bonds. The amount of unsaturated oil to be used is determined based on the weight of the saturated oil used, and should be in the range from about 1% to about 20% by weight. An amount of unsaturated oil from about 5% to about 10% by weight of the saturated oil-unsaturated oil mixture is preferred. The amount of unsaturated oil may be adjusted within the above ranges by one skilled in the art to achieve a desired drying rate.

The saturated oil-unsaturated oil mixture should be present in the ink compositions of the present invention in a weight ratio of carbon black dispersion to saturated oil-unsaturated oil mixture of about 1:0.9 to about 1:2.25. A carbon black composition/saturated oil-unsaturated oil mixture weight ratio of 1:2 is preferred.

Other Oil Phase Components

A non-ionic emulsifier can also be used in the ink compositions of the present invention to keep the ink composition stable and to reduce the surface tension energy of the oil phase, thereby increasing the drying rate of the ink. Useful non-ionic emulsifiers include sorbitan monooleate, which is available from ICI-American, and sorbitan trioleate, available from Witco Chemical Company. Sorbitan monooleate is preferred. The emulsifier is usually present in a weight ratio of non-ionic emulsifier to the saturated and unsaturated oil mixture of about 1:1.8 to about 1:9.5. An emulsifier/saturated and unsaturated oil mixture weight ratio of approximately 1:3.11 is preferred.

Varnishes may also be present in the oil phase of the ink compositions of the present invention to keep the carbon black stable on the paper fibers, to control the viscosity of the ink composition, and to control its diffusion on paper. Varnishes useful in the ink compositions of the present invention include modified resins and phenolic resins, and a mixture of Gum Rosin (available from Glidden Co.) and Tufflo-2000, wherein the Gum Rosin is present in an amount of 20.6% by weight of the varnish composition. Vehicle #3 is preferred. The varnish is usually present in a weight ratio of varnish to unsaturated and unsaturated oil of about 1:2.3 to about 1:9.5. A varnish/saturated and unsaturated oil mixture weight ratio of approximately 1:4.7 is preferred.

Anionic emulsifier may also be present in the oil phase of the present invention to increase the stability of the ink composition, in cooperation with the non-ionic emulsifier, and to reduce the surface tension of the ink compositions of the present invention, thereby promoting drying of the ink composition after it is applied to the surface of paper. Useful anionic emulsifiers include amine dodecylbenzene sulfonate (available from Stepan Chemical Co.), and calcium dodecylbenzene sulfonate (available from Witco). Amine dodecylbenzene sulfonate is preferred. The anionic emulsifier is usually present in a weight ratio of anionic emulsifier to saturated and unsaturated oil mixture of about 1:3.5 to about 1:14. An anionic emulsifier/saturated and unsaturated oil mixture weight ratio of approximately 1:7 is preferred.

Viscosity adjusting agents may also be used in the oil phase of the ink compositions of the present invention. The viscosity adjusting agents are used to control the viscosity of the ink compositions of the present invention and to aid migration of the carbon black particles into the paper after application of the ink. Useful viscosity adjusting agents include mineral seal oil (available from Rensberger Oil Co.), and other low viscose napthenic oils. Mineral seal oil is preferred. The viscosity adjusting agent is usually present in a weight ratio of viscosity adjusting agent to saturated and unsaturated oil mixture of about 0:3 to about 1:1. A viscosity adjusting agent/saturated and unsaturated oil mixture weight ratio of approximately 1:7 is preferred.

General Considerations

The viscosity and surface tension of a given ink composition can be adjusted depending upon the specific components used therein, and such adjustment is within the skill of those in the art.

Printed images may be generated with the ink compositions of the present invention by incorporating the inks into a commercial digital duplicating machine, and causing the ink to contact a paper substrate via a cylinder which is in contact with the paper substrate. Suitable duplicating machines for employing the ink compositions of the present invention include commercially available duplicating machines, such as the PrinTech 6720, available from A. B. Dick Company.

The ink compositions of the present invention can be applied to a variety of paper substrates, and exhibit improved drying times over prior art compositions on all types of paper substrates.

The present invention is further illustrated by the following examples.

Comparative Example 1

Commercially available ink compositions were tested for drying time on both opaque mimeo paper (available from A. B. Dick Company) and Red Label 20 lb. (available from A. B. Dick Company). The test procedure was as follows: The inks were printed on the papers through stencils (#2360, available from A. B. Dick Company), which were prepared by electronic photo stencil maker model (#595, available from A. B. Dick Company) equipped with a stylus (#481, available from A. B. Dick Company), using a rubber roller. The printed images were then rubbed every 20 seconds with white Kleenex™ papers, and the drying time was determined as the time when the rubbing did not smear the images and did not result in the transfer of any carbon black to the Kleenex paper.

Three commercially available water-in-oil emulsion ink compositions were tested: ink having the trademark #3400, available from A. B. Dick Company; ink having the trademark 1-1035-C, available from Riso Kagaku Corporation; and ink having the trademark VT-Black-800, available from Ricoh. The results are set forth in Table 1.

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Drying Time (seconds) of

Commercially Available Inks on Papers

Ink

Paper #3400 1-1035-C VT-Black-800

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Opaque Mimeo

210 190 150

Red Label 590 570 220

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Comparative Example 2

Ink compositions were formulated without oxidation of the carbon black pigment contained therein and using China-wood oil as the unsaturated oil. These ink compositions were tested for drying time on both opaque mimeo and Red Label paper. The amount of the components of these inks was as follows:

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Weight Ratio of Oil and Water Phases

Component Weight (grams)

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Oil Phase

China-wood oil in Tufflo-2000

2.8

Sorbitan monooleate 0.9

Vehicle #3 0.6

Amine dodecylbenzene sulfonate

0.4

Mineral seal oil 0.4

Water Phase

Carbon black dispersion

1.4

Deionized water 3.3

Total 9.8

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The carbon black dispersions tested were Permablack 292, Permablack 1180, AJACK BLACK 3017, and AJACK BLACK 3018. The inks were applied and the drying time measured as is set forth in Comparative Example 1 above. The results are set forth in Table 3.

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Drying Time (seconds) of Inks Without Oxided Carbon Black

Concentration of China-

Carbon Black wood Oil in Tufflo-2000

Paper Dispersion 0 Wt. % 5 Wt. %

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Opaque Mimeo

Permablack 292 170 30

Red Label 390 940

Opaque Mimeo

Permablack 1180

140 --

Red Label 420 --

Opaque Mimeo

AJACK BLACK 3017

60 40

Red Label 300 260

Opaque Mimeo

AJACK BLACK 3018

40 20

Red Label 300 160

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Comparative Example 3

Ink compositions were formulated without oxidation of the carbon black pigment and using aged linseed oil as the unsaturated oil. These compositions were then tested for drying time on both opaque mimeo and Red Label paper. The amount of the components of these inks was as follows:

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Weight Ratio of Oil and Water Phases

Component Weight (grams)

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Oil Phase

Aged linseed oil in Tufflo-2000

2.8

Sorbitan monooleate 0.9

Vehicle #3 0.6

Amine dodecylbenzene sulfonate

0.4

Mineral seal oil 0.4

Water Phase

Carbon black dispersion

1.4

Deionized water 3.3

Total 9.8

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The carbon black dispersions tested were Permablack 292, and AJACK BLACK 3018. The inks were applied and the drying times were measured as is set forth in Comparative Example 1 above. The results are shown in Table 5.

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Drying Time (seconds) of Inks With Aged Linseed Oil

Concentration of Aged

Linseed Oil In

Tufflo-2000

Carbon Black 0 Wt. 5 Wt. 20 wt.

Paper Dispersion % % %

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Opaque Mimeo

Permablack 292 170 500 230

Red Label 390 >1000 260

Opaque Mimeo

AJACK BLACK 3018

40 40 20

Red Label 300 300 180

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Preoxidation

Permablack Permablack

Time 292 1180 3017 3018

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0.5 hours

260 160 260 260

1 day 200 140 200 60

2 days 100 100 100 80

3 days 60 80 120 70

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